High intensity arc lamps are devices that emit a high intensity beam. The lamps generally include a gas containing chamber, for example, a glass bulb, with an anode and cathode that are used to excite the gas (ionizable medium) within the chamber. An electrical discharge is generated between the anode and cathode to provide power to the excited (e.g. ionized) gas to sustain the light emitted by the ionized gas during operation of the light source.
FIG. 1 shows a pictorial view and a cross section of a low-wattage parabolic prior art Xenon lamp 100. The lamp is generally constructed of metal and ceramic. The fill gas, Xenon, is inert and nontoxic. The lamp subassemblies may be constructed with high-temperature brazes in fixtures that constrain the assemblies to tight dimensional tolerances. FIG. 2 shows some of these lamp subassemblies and fixtures after brazing.
Referring to FIG. 1 and FIG. 2, there are three main subassemblies in the prior art lamp 100: cathode; anode; and reflector. A cathode assembly 3a contains a lamp cathode 3b, a plurality of struts holding the cathode 3b to a window flange 3c, a window 3d, and getters 3e. The lamp cathode 3b is a small, pencil-shaped part made, for example, from thoriated tungsten. During operation, the cathode 3b emits electrons that migrate across a lamp arc gap and strike an anode 3g. The electrons are emitted thermionically from the cathode 3b, so the cathode tip must maintain a high temperature and low-electron-emission to function.
The cathode struts 3c hold the cathode 3b rigidly in place and conduct current to the cathode 3b. The lamp window 3d may be ground and polished single-crystal sapphire (AlO2). Sapphire allows thermal expansion of the window 3d to match the flange thermal expansion of the flange 3c so that a hermetic seal is maintained over a wide operating temperature range. The thermal conductivity of sapphire transports heat to the flange 3c of the lamp and distributes the heat evenly to avoid cracking the window 3d. The getters 3e are wrapped around the cathode 3b and placed on the struts. The getters 3e absorb contaminant gases that evolve in the lamp during operation and extend lamp life by preventing the contaminants from poisoning the cathode 3b and transporting unwanted materials onto a reflector 3k and window 3d. The anode assembly 3f is composed of the anode 3g, a base 3h, and tabulation 3i. The anode 3g is generally constructed from pure tungsten and is much blunter in shape than the cathode 3b. This shape is mostly the result of the discharge physics that causes the arc to spread at its positive electrical attachment point. The arc is typically somewhat conical in shape, with the point of the cone touching the cathode 3b and the base of the cone resting on the anode 3g. The anode 3g is larger than the cathode 3b, to conduct more heat. About 80% of the conducted waste heat in the lamp is conducted out through the anode 3g, and 20% is conducted through the cathode 3b. The anode is generally configured to have a lower thermal resistance path to the lamp heat sinks, so the lamp base 3h is relatively massive. The base 3h is constructed of iron or other thermally conductive material to conduct heat loads from the lamp anode 3g. The tabulation 3i is the port for evacuating the lamp 100 and filling it with Xenon gas. After filling, the tabulation 3i is sealed, for example, pinched or cold-welded with a hydraulic tool, so the lamp 100 is simultaneously sealed and cut off from a filling and processing station. The reflector assembly 3j includes the reflector 3k and two sleeves 31. The reflector 3k may be a nearly pure polycrystalline alumina body that is glazed with a high temperature material to give the reflector a specular surface. The reflector 3k is then sealed to its sleeves 31 and a reflective coating is applied to the glazed inner surface.
FIG. 3A shows a first perspective of a prior art cylindrical lamp 300. Two arms 345, 346 protrude outward from the sealed chamber 320. The arms 345, 346 house a pair of electrodes 390, 391, which protrude inward into the sealed chamber 320, and provide an electric field for ignition of the ionizable medium within the chamber 320. Electrical connections for the electrodes 390, 391 are provided at the ends of the arms 345, 346.
The chamber 320 has an ingress window 326 where laser light from a laser source (not shown) may enter the chamber 320. Similarly the chamber 320 has an egress window 328 where high intensity light from energized plasma may exit the chamber 320. Light from the laser is focused on the excited gas (plasma) to provide sustaining energy. The ionized media may be added to or removed from the chamber with a controlled high pressure valve 398.
FIG. 3B shows a second perspective of the cylindrical lamp 300, by rotating the view of FIG. 3A ninety degrees vertically. A controlled high pressure valve 398 is located substantially opposite the viewing window 310. FIG. 3C shows a second perspective of the cylindrical lamp 300, by rotating the view of FIG. 3B ninety degrees horizontally. In general, the interior profile of the chamber 320 matches the exterior profile of the chamber 320.
The heated gas may cause some turbulence within the chamber. Such turbulence may affect the plasma region, for example expanding, modulating or deforming the plasma region, or otherwise lead to some instability in the high intensity output light.
A significant amount of instability may be caused by the thermal gradients in the bulb and gravity, causing turbulence in the gas surrounding the plasma. Since the plasma itself typically reaches temperatures over 9,000 k, the surrounding xenon gas sees a significant temperature gradient which in combination with gravity contributes to heavy turbulence. This turbulence affects the spatial stability of the plasma and equally impacts the thermal energy exchange dynamics of the plasma which in turns directly modifies the conversion efficiency of the photons. Therefore, there is a need to address one or more of the above mentioned shortcomings.